1. Field of the Invention
The present invention relates to a system and method for avoiding trailing artifacts in block processed video images.
2. Description of the Prior Art
There is an increasing reliance on video data in rich media applications running on interconnected devices or systems such as personal computers, wireless devices, surveillance systems, video conferencing systems and set-top boxes. Video data compression systems play a key role in increasing the efficiency of video data transmission. Video data is compressed or coded for transmission by taking advantage of the spatial redundancies within a given frame and the temporal redundancies between successive frames. Intraframe compression operates on single frames independently of other frames to exploit spatial redundancies within the frame, whereas interframe compression exploits both spatial and temporal redundancies.
Video compression systems exploit temporal redundancies using interframe prediction coding. Interframe coding is based on predicting the current source frame using the previously coded frame, and coding only the prediction error between the source frame and the predicted frame. Approximations are done in the prediction process, by assuming the motion is uniform across all pixels of each motion estimation block in each frame. It is noted that intercoding can be done for both uni-directional and bi-directional prediction. Transmission efficiencies are realised in interceding by transmitting the prediction error, as the amount of information present in the prediction error is generally less than that in the actual pixel values. However, when the prediction errors are not accurately reproduced by the coding process, a number of artifacts appear in the reconstructed video image. Trailing artifacts are an example of such artifacts and are related to motion in successive source frames. More specifically, trailing artifacts are directly related to situations where edges of a moving object in the video data fall on the edge pixels in the source blocks of the source frames, and appear as a series of dots or a series of groups of pixels that trail the moving object in the reconstructed frame. The artifacts can occur due to a coding skip, where the prediction error corresponding to a given source block is not coded, and/or coding of the prediction error with a large quantization value. The appearance of trailing artifacts can lead to a degradation in the quality of the video image. The problem can be more pronounced when trailing artifacts appear in flat areas of the image that do not have much spatial details, since such artifacts could be easily detected by the human eye in such areas.
It is an object of the present invention to provide a trailing artifact avoidance system and method to obviate or mitigate some of the above-presented disadvantages.